Tax breaks for married couples will be introduced by David Cameron before the next election, according to a Treasury minister.
David Gauke has moved to reassure Tory backbenchers amid growing concern in the party about how much support is being offered to traditional families.
In a letter to Conservative MPs, he insisted the change would go ahead during this parliament - meaning it will happen in the next two years.
The step is designed to avoid another backbench rebellion as Tories are currently trying to force the issue by introducing an amendment to the Finance Bill.
Mr Gauke wrote: "The Prime Minister and Chancellor have consistently made clear that we remain committed to recognising marriage in the tax system.
"I know that many of you will have heard the Chancellor set out his commitment to deliver on this during the course of this parliament.
"An announcement on details of how we will legislate for this in this parliament will be made by the Chancellor in due course."
Under the Tory plan, spouses who do not work could transfer part of their tax-free allowance if their partner earned less than the basic rate of tax.
It is thought the change would be worth up to £150 to married couples, meaning its significance would be largely symbolic.
But it would go some way to easing anger about the coalition's approach to stay-at-home mothers, who have been hit by restrictions on childcare support and child benefit cuts.
MPs welcomed the reiteration of Mr Cameron's commitment to the policy, but pushed for a clearer timetable for its introduction.
Former education minister Tim Loughton, who is leading the backbench revolt, told The Telegraph: "There is only a certain amount of promises about 'in due course' that hard-working families can take.
"This was a clear Conservative manifesto commitment to deliver a clear and popular Conservative policy that rights an injustice by recognising hard-working families in the tax system."
A limited tax break was offered in the Tory election manifesto in 2010 and a commitment to hold a vote on the measure by 2015 was included in the coalition agreement.
The document allows the Lib Dems, who oppose the measure, to abstain.
Government sources are reported to have indicated the change is likely to be tabled in April 2015, which would coincide with general election campaigning.
But is is also considered possible that it could be legislated on in this parliament with implementation delayed.
Mr Cameron's official spokesman confirmed George Osborne intended to bring forward legislation before the end of the parliament but refused to give any clearer timetable.
He also refused to clarify whether the change could come into effect before or after the election.
Sky's deputy political editor Joey Jones said: "Whether or not that will satisfy some increasingly impatient colleagues, we will only find out in the next couple of weeks."
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